In vivo trafficking of endogenous opioid receptors.
Several approaches have been taken for these in vivo studies. In many studies, the use of semi-quantitative immuno-electron microscopy is the approach of choice. Endogenous opioid receptors display differential subcellular distributions with mu opioid receptor (MOPR) being mostly present on the plasma membrane and delta-opioid receptor (DOPR) and kappa-opioid receptor (KOPR) having a significant intracellular pool. Etorphine and DAMGO cause endocytosis of the MOPR, but morphine does not, except in some dendrites. Interestingly, chronic inflammatory pain and morphine treatment promote trafficking of intracellular DOPR to the cell surface which may account for the enhanced antinociceptive effects of DOPR agonists. KOPR has been reported to be associated with secretory vesicles in the posterior pituitary and translocated to the cell surface upon salt loading along with the release of vasopressin. The study of endogenous opioid receptors using in vivo models has produced some interesting results that could not have been anticipated in vitro. In vivo studies, therefore, are essential to provide insight into the mechanisms underlying opioid receptor regulation.
Wang
Yulin
Y
Department of Pharmacology and Center for Substance Abuse Research, Temple University School of Medicine, 3420 North Broad Street, Philadelphia, PA 19140, USA.
Van Bockstaele
Elisabeth J
EJ
Liu-Chen
Lee-Yuan
LY
D000701:Analgesics, Opioid / Q000494:pharmacology; D000818:Animals; D006801:Humans; D018847:Opioid Peptides / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D011956:Receptors, Cell Surface / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D017465:Receptors, Opioid, delta / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D017473:Receptors, Opioid, kappa / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D017450:Receptors, Opioid, mu / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D015398:Signal Transduction; D013347:Subcellular Fractions
D000701:Analgesics, Opioid; D018847:Opioid Peptides; D011956:Receptors, Cell Surface; D017465:Receptors, Opioid, delta; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu